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Using Blatant Code, a New Nokoyawa Variant Sneaks up on Peers

 

Nokoyawa is a new malware for Windows that first appeared early this year. The first samples gathered by FortiGuard researchers were constructed in February 2022 and contain significant coding similarities with Karma ransomware that can be traced back to Nemty via a long series of variants. 

NOKOYAWA is a ransomware-type piece of malware that the research team discovered and sampled from VirusTotal. It's made to encrypt data and then demands payment to decode it. 

FortiGuard Labs has seen versions constructed to run only on 64-bit Windows, unlike its precursor Karma, which runs on both 32-bit and 64-bit Windows. For customized executions, Nokoyawa provides many command-line options: help, network, document, and Encrypt a single file using the path and dir dirPath. 

Nokoyawa encrypts all local disks and volumes by default if no argument is provided. The "-help" argument is intriguing because it shows that the ransomware creators and the operators who deploy and execute the malware on affected PCs are two independent teams. Nokoyawa encrypts files that do not end in.exe,.dll, or.lnk extensions using multiple threads for speed and efficiency. Furthermore, by verifying the hash of its names with a list of hardcoded hashes, some folders, and their subdirectories are prohibited from encryption.

Nokoyawa produces a fresh ephemeral keypair (victim file keys) for each file before encrypting it. A 64-byte shared secret is produced with Elliptic-Curve Diffie-Hellmann using the victim file's private key and the threat actors' "master" public key (ECDH). For encrypting the contents of each file, the first 32 bytes of this secret key are used as a Salsa20 key, together with the hardcoded nonce 'lvcelvce.' 

RURansom, A1tft, Kashima, and pEaKyBlNdEr are just a few of the ransomware programs that have been looked into. The encryption algorithms they utilize (symmetric or asymmetric) and the ransom size are two key variations between malicious applications of this type. The magnitude of the requested sum can vary dramatically depending on the intended victim. 

How does ransomware get into my system? 

The majority of the additional code was taken exactly from publicly available sources, including the source of the now-defunct Babuk ransomware leaked in September 2021, according to FortiGuard Labs experts. 

Malware including ransomware is spread using phishing and social engineering techniques. Malicious software is frequently disguised as or integrated with legitimate files. 

The email addresses were eliminated and were replaced with directions to contact the ransomware authors using a TOR browser and a.onion URL. When you're at the Onion URL, you'll be taken to a page with an online chatbox where you can chat with the operators, negotiate and pay the ransom. 

Researchers from FortiGuard Labs detected a dialogue between a potential victim and the ransomware operator. The threat actors offer free decryption of up to three files based on this chat history to demonstrate that they can decrypt the victim's files.

The ransom amount, in this case, a whopping 1,500,000 (likely in USD), is displayed on the "Instructions" page and can be paid in either BTC (Bitcoin) or XMR(Monero). The operators claim to deliver the tool to decrypt the victim's files after payment.

Given the rising professionalism of certain ransomware efforts, this TOR website could be an attempt to better "branding" or a technique to delegate ransom discussions to a separate team. Surprisingly, the ransom note contains the following content. "Contact us to strike a deal or we'll publish your black s**t to the media," the message says, implying that the victim's data was stolen during the infection.

Drive-by (stealthy and deceptive) downloads, spam email (malicious files attached to or compromised websites linked in emails/messages), untrustworthy download channels (e.g., peer-to-peer sharing networks, unofficial and freeware sites, etc.), illegal software activation ("cracking") tools, online scams, and fake updates are among the most common distribution methods. 

How can we defend from ransomware?

It is strongly advised you only use legitimate and trusted download sources. Furthermore, all apps must be activated and updated through tools given by genuine providers, as third-party tools may infect the system. 

Experts also recommend against opening attachments or links received in questionable emails or messages, as they may contain malware. It is critical to install and maintain a reliable anti-virus program. 

Regular system scans and threats/issues must be removed using security software. If the machine has already been infected with NOKOYAWA, we recommend using Combo Cleaner Antivirus for Windows to automatically remove it.

Microsoft Office Users Targeted in a New Zero-Day Attack

 

Microsoft issued a warning to Windows users on Tuesday that attackers are actively exploiting an unpatched remote execution zero-day vulnerability in MSHTML, a proprietary browser engine for the now-discontinued Internet Explorer using weaponized MS Office documents. 

Tracked as CVE-2021-40444, the vulnerability affects Windows Server 2008 through 2019 and Windows 8.1 through 10 and has a severity level of 8.8 out of the maximum 10.

"Microsoft is investigating reports of a remote code execution vulnerability in MSHTML that affects Microsoft Windows. Microsoft is aware of targeted attacks that attempt to exploit this vulnerability by using specially-crafted Microsoft Office documents," the company said in a security advisory. 

"An attacker could craft a malicious ActiveX control to be used by a Microsoft Office document that hosts the browser rendering engine. The attacker would then have to convince the user to open the malicious document. Users whose accounts are configured to have fewer user rights on the system could be less impacted than users who operate with administrative user rights," it added.

ActiveX is a software framework from Microsoft that adapts its earlier Component Object Model and Object Linking and Embedding technologies for content downloaded from a network. 

Microsoft credited researchers from EXPMON and Mandiant for reporting the flaw, although the company did not provide further details about the nature of the attacks, the identity of the adversaries exploiting this zero-day, or their targets in light of real-world attacks. 

The researchers at EXPMON stated they discovered the issue after detecting a "highly sophisticated zero-day attack" directed at Microsoft Office users, adding they shared the findings with Microsoft on Sunday. "The exploit uses logical flaws so the exploitation is perfectly reliable (& dangerous)," EXPMON researchers said. 

However, the risk can be mitigated if Microsoft Office operates with default configurations, wherein documents downloaded from the web are opened in Protected View or Application Guard for Office, which is designed to prevent untrusted files from accessing trusted resources in the compromised system. 

Microsoft, upon completion of the investigation, is expected to publish a security patch or an out-of-cycle security update as part of its Patch Tuesday monthly release cycle "depending on customer needs." In the interim, the Windows maker is advising users and organizations to disable all ActiveX controls in Internet Explorer to mitigate any potential threat.